It is known to provide a multi-axle vehicle in which the engine transmits power to a plurality of axles, each of which have at least one wheel and generally a pair of wheels for propelling the vehicle.
Such vehicles include so-called tractors, which can be provided with clutches selectively enabling the front axle to be coupled with the speed-changing transmission, which is provided between the axle and the engine.
Tractors of this type are provided with parking brakes which can be arranged either on the main drive axle or on the transmission. Such parking brakes have in common the fact that they are effective only upon the main drive axle, for example the rear axle which generally is continuously coupled with the transmission and engine.
As trucks and tractors for semitrailers or full trailers must be capable of displacing increasing loads, there has been a substantial increase in the development of front axle drives. It has thus become necessary to ensure that the parking brake or locking brakes will also be effective for the drivable front axle wheels as well.
In the aforementioned copending application, the problem of providing a parking brake for such multi-axle vehicles and especially vehicles which have a permanently driven rear axle and a clutch for the selective coupling of a front axle to the engine has been described. The mechanism which solves this problem comprises a main shaft, a drive wheel nonrotatably mounted on the main shaft, the clutch disk carrier nonrotatable but axially movable with respect to the drive wheel, whereby the main shaft can be brought into engagement with the drive wheel, and a parking brake lockable with respect to the drive wheel and the disk carrier.
This enables all of the drivable axle to be locked by the operation of the parking brake without having to consider the position of the clutch for the axle which is selectively engageable.
Thus, this arrangement provides a parking brake which shares the same housing as the clutch, which is allocated to the selectively operable drive axle, so that this parking brake connects the main drive axle and the selectively operable axle with the common housing when the clutch connects the selectively operable axle with the drive.
This arrangement has been found to be highly effective for modern tractors with high-front-end loading because both the front and rear axles are locked in a single operation.
While this system has been found to be fully effective, simplification, and structural and maintenance requirements have induced research into further improvements.